docs: documented page maps

.wiki/Kernel-documentation.md

@@ -99,6 +99,75 @@ This is kind of the low level version of free.
 #### `pframe_free_multi(address, n)` - function (void) [Thread Safe]
 Frees the page at the given address, plus *n* pages after that page.
 
+### page_map.h
+
+#### `VIRTUAL_ADDRESS_MAX` - macro
+The highest mappable virtual address.
+4 level page maps have a maximum address space of 256TB.
+
+#### `page_map_flag_E` - enum
+  - **Present** - This indicates if the entry is used or should be ignored. Automatically set when mapping a page.
+  - **Read & Write** - A mapped Page is always readable. This flag allows writing to that page.
+  - **User Super** - If set, user mode access to the page is allowed.
+  - **Write Through** - Enables _Write Through Caching_ for this page.
+  - **Cache Disabled** - If this bit is set, the page won't be cached.
+  - **Accessed** - Set by the CPU, when this PDE or PTE was read. Won't be reset by the CPU.
+  - **Larger Pages** - Set when the page has been modified.
+  - **Custom 1 - 3** - Not used in NoxOS.
+  - **No Execute** - When this bit is set, the CPU won't execute code that lies in that page.
+
+#### `page_map_T` - struct [page aligned]
+This struct contains 512 entries.
+These entries contain an address and flags.
+The addresses link like this:
+  - **PML4** --> **Page Directory** or _1GB Page_
+  - **Page Directory** --> **Page Table** or _2MB Page_
+  - **Page Table** --> _4KB Page_
+
+A pointer to a `page_map_T` can be loaded into `cr3` to load this pagemap.
+
+#### `page_map_create()` - function (page_map_T*)
+Allocates a `page_map_T` and returns a pointer to it.
+
+#### `page_map_fetch_current()` - function (page_map_T*) [ASM implementation]
+This function will return the page map, that is currently loaded.
+To achieve this, it just reads the `cr3` value.
+
+#### `page_map_load(page_map*)` - function (void) [ASM implementation]
+Loads the given page map.
+To achieve this, it writes the `cr3` value.
+
+#### `page_map_map_memory(page_map*, virtual_address, physical_address, flags)` - function (void)
+This maps **_physical_address_** to **_virtual_address_** in **_page_map_**.
+The **_flags_** will be applied to the page mapping / page table entry.
+It always applies the _Present_ flag.
+
+#### `page_map_unmap_memory(page_map*, virtual_address)` - function (void)
+Removes a page mapping from the **_page_map_**.
+Page map structure intern pages won't be checked if they're still needed or not.
+
+#### `page_map_destruct(page_map*)` - function (void)
+Clears a page map and frees all page map structure intern pages.
+
+#### `page_map_entry_set_flags(entry, uint64_t flags)` - function (void)
+This will set the provided flags to a page map entry.
+
+#### `page_map_entry_get_flag(entry, page_map_flag_E flag)` - function (bool)
+Returns if the given flag is set in the page map entry, or not.
+
+#### `page_map_entry_set_address(entry, void* address)` - function (void)
+This will set the provided address to a page map entry.
+
+#### `page_map_entry_get_address(entry)` - function (void*)
+This will read and return the address set in the page map entry.
+
+#### `paging_init()` - function (void)
+Initializes paging.
+This reads the current page map set by the kernel and writes it to `g_kernel_page_map`.
+
+#### `g_kernel_page_map` - global variable
+The kernels page map. This page map is provided by the bootloader and read from `cr3` at `paging_init`.
+
 ## platform
 
 ### cpu.h